Such a heat exchanger is for example known from DE 10 2004 030 675 A1. For cooling of electronic components, which are arranged within a switch cabinet, there is formed a channel together with a wall of the switch cabinet, and a medium such as air flows through the channel. The channel has an inlet for cool air and an outlet for heated air. Cooling elements are arranged on a channel wall, which shall provide for a better heat transfer from that wall to the air flowing along it.
Heat exchangers having successively arranged stages where each stage is fed with fresh medium are known from US 2004/0256092 A1 and US 2002/0000311 A1.
Generally, the heat flow WF flowing along a surface A is proportional to the temperature difference ΔT between the fluid and the surface A. As a proportiona-lity constant α the heat transfer coefficient in [W/m2*K] is chosen and therefore, it is valid:WF=α*A*ΔT  i.
The heat transfer coefficient α is dependent on material constants as well as from the aforementioned cooling elements, which for example provoke a turbulence.
From the above equation it can be seen that the cooling performance is proportional to the temperature difference ΔT. Where the flow path of the cooling fluid is longer, the cooling fluid is heated such that the temperature difference along the flow path decreases and thereby the cooling performance decreases.
It is mentioned that analogous relationships are naturally valid for a heating, as for example a hot medium shall transmit heat to another object, as for example to a plate. If in the following the words cooling or cooling efficiency are used, the same is also true in an analogous manner for heating and heating efficiency.
As shown in the above mentioned prior art, it is often necessary to cool or heat elongated surfaces, wherein the problem of the decreasing cooling efficiency with increasing length arises.
A possibility for solving this problem is to increase the flow velocity of the fluid and therewith the flow rate of the fluid. This, however, requires greater dimensioned feeding devices for the fluid, thus for example greater dimensioned blowers, which causes higher driving energy and therewith mostly a higher electrical current consumption as well as an increased required space and finally also a higher noise emission.